1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method of the same.
2. Description of the Related Art
In a manufacturing process of semiconductor devices, a plurality of patterns, such as an active region, an electrode, etc., are formed one after another. Thus, in a semiconductor device, a mask which has a pattern to be formed after a-previously-formed pattern needs to be arranged in an appropriate position.
For example, in a lithography process, a photomask is aligned in a predetermined position by using an alignment mark, which is formed on a semiconductor substrate. Specifically, laser is applied to the alignment mark, such as a diffraction grating or the like. In order to detect the alignment mark, a waveform of diffracted light is used, thereby the photomask can be arranged.
As the semiconductor device fabrication process becomes more and more complicated, it is difficult to retain the alignment mark in a desired state. For example, if the diffraction grating is used as the alignment mark, a film formed on the alignment mark tends to remain thereon, when patterning the film. Therefore, the form of the alignment mark may not desirably be retained.
In a case where a trench which has been made for performing shallow trench isolation (a technique for electronically isolating elements on the semiconductor substrate, by forming a trench and filling the trench with insulating materials) is used as an alignment mark, it is still difficult to retain the desirable form of the alignment mark. When a gate electrode is formed, a polycide is to be formed on the semiconductor substrate with the alignment mark. The gate electrode is formed by patterning the polycide by performing photolithography. In patterning the polycide, anisotropic etching is performed thereto. If the polycide is formed in the trench, the polycide may not completely be removed therefrom by the anisotropic etching, owing to the depth of the trench (alignment mark) for the shallow trench isolation. The amount of each polycide remaining in the trench may vary, because an etching rate of the anisotropic etching varies. That is, the form of the alignment mark may not preferably be retained after the formation of the gate electrode.
If the form of the alignment is not retained desirably, the alignment of subsequent mask may become inaccurate. As a result, the semiconductor device may be manufactured with a low degree of reliability, and the yield of such semiconductor devices is low.